‘GS 66’ is a new and distinct variety of apple tree (Malus domestica) of unknown parentage. ‘GS 66’ originated from an open cross in 2008 in a commercial orchard at Wendhausen, Germany in 2008, and was identified by the inventor as a candidate for further evaluation in 2012. ‘GS 66’ was first asexually reproduced by table grafting at Wendhausen, Germany in 2013, and has since been observed to remain true to type over successive asexually propagated generations.